The present invention relates to a process for preparing a polymerizable (meth) acrylate oligomer. More particularly, the invention relates to a new process for preparing a polymerizable (meth) acrylate oligomer containing an acryloyl group and an unsaturated alicyclic dicarboxyl group in the molecule.
Various types of polymerizable acrylates have been known and used as a heat-, photo- or electron-curable resins in the preparation of coatings, adhesives, reinforced plastics and the like. For example, an epoxy acrylate has been obtained by reacting a polyglycidylether of a polyhydric phenol having more than one epoxy group per molecule with an acrylic acid (see U.S. Pat. Nos. 2,824,851, 3,179,623, 3,377,406, 3,432,478 and 3,317,465). Also, the acrylate which is obtained by reacting a polyglycidylester of a polybasic acid with an acrylic acid has been disclosed in U.S. Pat. No. 3,808,114.
Recently, it has been found that it is possible to obtain a useful polymerizable (meth) acrylate oligomer containing an acryloyl and an unsaturated alicyclic dicarboxyl group in the molecule by reacting an epoxide with a carboxylic acid, wherein at least one of said compounds contains an unsaturated alicyclic dicarboxyl group and the other one contains an acryloyl group. The oligomer excels in providing a tack-free surface in air in a cured state, compared to conventional resins such as unsaturated polyesters and vinyl ester resins (e.g. epoxy acrylates).
As a result, when the oligomer is used in coatings, the coating obtained from the oligomer provides not only a tack-free surface but also provides excellent adhesion to a substrate after curing.
However, since the oligomer contains in close proximity both a highly oxidizable unsaturated alicyclic nucleus which readily forms a hydroperoxide and a highly polymerizable acryloyl group, gelation (crosslinking) is almost completed in the period of the reaction under well known conditions. Gelation takes place readily in the synthesis of an oligomer in which a carboxyl group of the unsaturated alicyclic dicarboxyl group compound and a carboxyl group of the acryloyl group compound combine to form an ester-bond with a polyhydric alcohol having 2 to 4 carbon atoms.